To add a community agency to your organization's Legacy agencies simply take the following steps:
Find a candidate submitted by the agency you want to add as a legacy, click on that candidate's name to open their card.
Then go to the "Chat" tab on that candidate's card.
Click on the Agency Recruiter's name at the top of the conversation (see below), this will open the Agency Recruiter's drawer.
From there click on the action menu located in the top right of the drawer.
Select "Add As Legacy" and then select the fee you want to add them at and they are now a legacy agency for your organization.
Note: Adding an agency as a legacy not only adds the individual recruiter but their whole team.